Piezo Input ADC and Digital IN

Right now just using 5 channels, using real cymbals that are duct taped for the time being.

If I could use a transistor, that'd be great, or op-amp even. I am a visual kind of person, I saw an example of signaling a digital input where it looked like they had connected the pin to negative to signal low - is that how it's done? What I am not picturing is how that could be accomplished using the components as the output would be close to vcc voltage. If I can tie the digital pin to the output of the op-amp or transistor, then I think that would get me a lot closer. Any thoughts on using a schmitt trigger?

Thanks,
Pete